The present invention generally relates to sockets for IC chips, and more particularly to the construction of cover assemblies for IC sockets which hold the input/output (I/O) contacts of an IC chip in electrical contact with the compliant tips of an array of conductive probes.
Sockets for holding IC chips are well known and widely used in a variety of industrial applications for achieving efficient electrical contact between the I/O contacts of an IC chip and the conductors of a connector, circuit board, or the like. Such applications include test sockets for testing IC devices and contactor sockets for removably mounting an IC device to a printed circuit board. The basic function of the socket is to hold the IC chip in a fixed position such that the array of I/O contacts can be contacted by the compliant tips of a corresponding pogo pin array to produce a desired electrical connection. Precise orientation of the IC chip in the socket is critical to this function and generally to the electrical and mechanical performance of the socket. One aspect of this orientation is to maintain the chip in a true x-y plane as the chip is pressed in the z-axis against the compliant tips of the socket""s probe array. Any tilting or canting of the chip from its desired x-y orientation can cause the chip, or a floating platform holding the chip, to bind up in the socket and can prevent the desired electrical interface with each and all of the I/O contacts of the chip.
Socket covers generally provide for a protruding structure that is integral with the underside of the cover and that is positioned and formed to contact and depress the IC chip in a cavity within the IC socket when the cover is operatively attached to the top of the socket. Conventionally, the socket cover is either separate from the socket or hinged to the socket. In either case, as the socket cover is moved to its closed position, slight misalignments occur between the socket and socket cover which are detrimental to maintaining the x-y positioning of the chip in the socket. For a hinged cover, this alignment is due to the fact that the depressor structure on the underside of the cover contacts the IC chip before the cover reaches a fully rotated closed position. At this point of contact, the force of the cover pushing against the chip is not a true normal force in reference to the x-y plane of the chip. In a separately attached cover that is not hinged to the socket, misalignments will occur when a cover is placed by hand over the socket at any angle of attack that is not precisely normal to the socket""s x-y plane.
The present invention provides a cover assembly for an IC socket that overcomes the aforementioned disadvantages of conventional socket cover designs. The invention specifically provides a socket cover assembly that permits a depressor member on the underside of the socket cover to contact the IC chip held in the socket at an angle of attack that is precisely controlled, and that prevents misalignment between the axis of the socket and the force vector applied by the cover""s depressor member against the IC chip. The invention will minimize any tendency of the chip or chip platform to tilt within the socket thereby improving the socket""s overall electrical and mechanical performance.
Briefly, the invention is a cover assembly for operatively holding an IC chip in a chip cavity of an IC socket wherein the chip cavity extends into a top face of the IC socket along a defined z-axis. The cover assembly includes a lid portion having a top side, an underside, and a defined z-axis, and mounting means for mounting the lid portion in an operative position on the IC socket. The mounting means includes cover locking means for locking the lid portion of the cover assembly in an operative closed position in which the z-axis of the lid portion aligns with the z-axis of the chip cavity. The lid portion is provided with a retractable chip depressor member extendable from the underside of the lid portion along the lid""s z-axis. When the lid portion is in its operative closed position over the chip cavity of the socket, the retractable chip depressor member is advanced along the z-axis by a depressor actuation means accessible from the top side of the lid portion, whereby the chip is at all times depressed in the IC socket by a force parallel to the z-axis of the chip cavity and normal to the IC chip.
In one aspect of the invention, the mounting means of the cover assembly includes slide rails for slidably engaging corresponding locking channels formed in the IC socket to which the lid portion is mounted. The slide rails are pivotally connected to the lid portion such that, when the slide rails are engaged in the locking channels of the socket, the lid portion can be pivoted on the slide rails into its operative close position.
In another aspect of the invention, the mounting means includes a mounting frame which is likewise pivotally connected to the lid portion of the cover assembly. The mounting frame has fastening means for fastening the frame to the top face of the socket such that, when the mounting frame is fastened to the socket, the lid portion can be pivoted on the mounting frame into its operative closed position. This embodiment has particular utility where space considerations are paramount, since an entire cover assembly can be provided which matches the footprint of the socket.
The invention also contemplates a mounting means that permit the lid portion of the cover assembly to be directly fastened to the IC socket such as by a releasable clip lock means that engage a corresponding clip lock engagement structure on the IC socket.
The depressor actuation means can suitably be provided by a cam mechanism for converting a rotational actuation motion imparted by a handle on the top side of the lid portion to a translational depressing motion of the depressor member in the z-axis of the lid portion. Alternatively, the lid portion of the cover assembly can be provided with a threaded guide hole and the chip depressor member and depressor actuation means can be provided in the form of a threaded cylinder threadedly engaged in the guide hole such that rotation of the threaded cylinder in the guide hole causes the cylinder to advance along the z-axis of the lid.
Finally, the invention includes a method of depressing an IC chip in a chip cavity of an IC socket having a z-axis normal to the plane of the IC chip held in the socket. The method is comprised of placing the IC chip in the chip cavity of the socket and then covering the IC chip with a cover assembly so as to achieve alignment with the z-axis of the chip cavity. From the cover assembly, the IC chip is then contacted and depressed in the IC cavity along the z-axis, such that the contact force is at all times normal to the IC chip.